1. Field of the Invention
This invention relates to a method of manufacturing a compound semiconductor by means of the molecular beam epitaxy (MBE).
2. Prior Art
The molecular beam epitaxy is widely used for manufacturing compound semiconductors.
As is known well, the MBE is a technique with which atoms of one or more than one components of the crystal of a semiconductor material are caused to hit a substrate as molecular beams in order to make the crystal grow on the substrate.
A very thin single crystal film can be made to grow in situ with MBE by controlling the composition of the crystal. Particularly, the crystal growth of a compound semiconductor can be realized on an atomic layer basis to produce semiconductor crystal having an evenly and finely distributed composition, if molecular beams of different kinds are fed to the substrate simultaneously in an highly controlled manner. This technique proves to be very advantageous in producing quantized devices.
Quantized devices produced by forming crystal of a semiconductor substance such as InAlAs, InGaAs or InGaAlAs on a substrate of a III-V compound, using MBE seem to be very promising, if they are used for semiconductor laser devices, photosensors and high-speed transistors.
Some of the requirements to be met in order to make high quality semiconductor crystal grow steadily and stably on a substrate of a III-V compound by means of MBE include a reduced transient in the intensity of molecular beams, a stabilized As pressure to be realized by controlling the back pressure and a clean substrate surface in a high vacuum atmosphere.
Therefore, the process of producing compound semiconductors with MBE typically involves a substrate cleaning operation.
In such a substrate cleaning operation, the substrate is most usually heated in order to remove impure substances from the surface of the substrate. However, the V group component of the substrate that can produce high-vapor pressure can also move away from the substrate during the operation to degrade the substrate surface and make the latter unsuitable for growing crystal.
A measure that has been proposed and is currently used to prevent the V group component from moving out of the substrate is evaporation of molecular beams of V molecules that do not significantly settle by themselves on the substrate, while heating the substrate surface.
For instance, an InP substrate is evaporated with As molecular beams to prevent P from leaving the substrate, while heating the substrate surface.